1. Field of the Invention
The present invention relates to a ceramic member for semiconductor manufacturing equipment which is formed of a ceramic material having a low dielectric loss and high corrosion resistance and, in particular, to a ceramic member having high strength and excellent machinability.
2. Prior Art
In semiconductor manufacturing Process, there have been used equipment for etching or cleaning a wafer therein by using halogen plasma, which is provided with members including, for example, an inner wail making up a chamber, a microwave-introducing window or inlet for introducing microwave into the chamber, a focus ring, a clamp ring for fixing a wafer to be treated on a stage or electrode, a susceptor and the like.
FIG. 1 shows as example of semiconductor manufacturing equipment, a processing chamber used for halogen-plasma etching or cleaning systems in producing semiconductor devices. This chamber includes a chamber wall 1, with a high frequency induction coil 6 arranged on the outside of the chamber to generate plasma in a space of the chamber, with a shower head 2 fixed at the upper portion inside the chamber wall 1 to supply a gas mixture containing a halogen gas into the chamber and with a lower electrode 4, or a stage, arranged at the lower portion in order to mount a wafer 5 to be processed thereon. Furthermore, a clamp ring 3 for fixing the wafer 5 is mounted on the lower electrode.
Excepting work pieces such as the semiconductor wafer to be processed, the members such as chamber wall 1, shower head 2 and clamp ring 3 have been made of corrosion-resistant material such as quartz, stainless steel, alumina or the like. Also, there have been utilized sintered materials of alumina or aluminum nitride, and materials obtained by coating these ceramic sintered materials with a ceramic film of silicon. Further, Such members of the semiconductor manufacturing equipment have conventionally been made of alumina-based sinters which have high corrosion resistance to gases containing fluorine or chlorine and are available at low prices.
While in such semiconductor manufacturing equipment, radio frequency or microwave is introduced into the reaction chamber to generate plasma of halogen, alumina-based sinters absorb so considerable large a part of RF wave or microwave input to generate heat. This in turn poses problems of causing plasma generation efficiency to deteriorate due to energy loss.
Moreover, another problem is that local heat generation within the ceramic body causes partial expansion of the body to form cracks in the alumina-based sintered member.
For this reason, alumina-based sinters have been required to have lower dielectric loss, and for example, Japanese Patent Laid-Open Publication NO. 5-217946 proposes a technique in which for a bell jar, a high-purity alumina-based sinter is used which contains reduced amounts of SiO2 and alkali metal oxide so that its dielectric loss levels at 1 GHz to 10 GHz may be lowered to be 8×10−4 or less (0.9×10−4 at the smallest). Also, Japanese Patent Laid-Open Publication No. 2001-28502 discloses a technique for an RF or microwave penetration window which is produced of a ceramic sintered body containing principally either an yttrium-aluminum-garnet (hereinafter, abbreviated as YAG) or alumina, and silicon oxide at an amount of between 0.1 to 10 wt %, thereby decreasing dielectric loss to the level of 5×10−3 or less at 10 MHz to 10 GHz.
Unfortunately, the alumina-based sinter as disclosed in the above Japanese Patent Laid-Open Publication NO. 5-217946 or the ceramic sinter disclosed in Japanese Patent Laid-Open Publication 2001-28502 have not so high strength as to be used for portions where high stress is applied without any shape constraints.
Also, in order to reduce energy absorption loss within members in semiconductor manufacturing equipment, it is required that the dielectric loss, in the wide frequency ranges of 10 MHz to 5 GHz, of the ceramic sinters comprising the members of the semiconductor manufacturing equipment should be reduced to as low a level as possible.
However, the ceramic material disclosed in Japanese Patent Laid-Open Publication 2001-28502 does not provide enough low dielectric loss, which is about 5×10−4 in a region of 10 MHz to 10 GHz even in a case of lowest loss. Therefore, further lower dielectric loss is required in such ceramic dielectric materials to be used for the above applications.
On the other hand, Japanese Patent Laid-Open Publication NO. 8-325054 discloses a dielectric material having lower dielectric loss. The ceramic sinter is composed principally of alumina with 0.5 wt % of yttrium oxide contained, layers of a Y2O3 or Al2O3—Y2O5 compound being formed between aluminum grain boundaries, thereby achieving dielectric loss of less than 1×10−4 levels at 7 GHz to 9 GHz.
It has been known that dielectric loss of ceramic sinters generally increases with a decrease in frequency from high-frequency microwave regions to radio frequency regions. while the above ceramic sinter as disclosed in Japanese Patent Laid-Open Publication NO. 8-325054 is actually very low in dielectric loss at the region of 7 GHz to 9 GHz, it increases in dielectric loss in the lower frequency regions, for Example, of 10 MHz to 5 GHz.
Still further, alumina powder used for manufacturing the above ceramic sinter have contained silicon oxide as an impurity and such ceramic sinter may have included foreign silicon oxide particles derived from the outside during ceramic manufacturing process. A considerable high level of silicon oxide may be accumulated as a non-careful impurity in the ceramic sintered body and such impurity has a risk of causing the dielectric loss at the region of 10 MHz to 5 GHz to further increase. Thus, with the ceramic sinter, sufficient reduction of energy loss due to the heat generation at RF or microwave region could not be attained so far.
Furthermore, the alumina-based sinters disclosed in Japanese Patent Laid-Open Publications NO. 5-217946, 2001-28502 and NO. 8-325054 are low in grindability with their large fracture toughness values, therefore taking long time in machining. Thus, such conventional alumina-based sinters have had an problem that long machining time would be reflected to raise cost of each ceramic member, resulting in high priced semiconductor manufacturing equipment. A ceramic sintered body composed principally of YAG is disclosed in Japanese Patent Laid-Open Publication 2001-28502, and the ceramic body, low in bending strength, poses the problem that it tends to be chipped or cracked easily in assembly or handling operation process.